Field
The present invention relates generally to electric power storage and generation. More particularly, the present invention provides a system for gravitational potential energy storage employing electrically driven rail consists carrying off loadable masses between lower and upper storage yards. Potential energy is stored by employing electrical grid power for transport of the masses from the lower to upper storage facility using motor powered winch sets. Potential energy is recovered and returned to the electrical grid by generator operation of the winch set motors during transport of the masses from the upper to lower storage yards. The invention allows for grid load shifting as well the full range of ancillary services including regulation, spin, non-spin, replacement reserves, blackstart, VAR and heavy inertia to the grid.
Related Art
The electric power grid is increasingly complex and the matching of power usage with power generation capabilities is a critical element in maintaining stability in operation. This issue is becoming more complicated with the addition of alternative energy generation sources such as wind power and solar power, which have inherent issues with consistency of power production. The need for utility scale energy storage as a portion of the power supply grid is driven by requirements for daily load shifting and power quality services including frequency regulation, voltage control, spinning reserve, non-spinning reserve and black start. It is presently estimated that requirements in the US will approach 85,000 MW for load shifting and 7,137 MW for power quality while global requirements will approach 450,000 MW for load shifting and 37,828 MW for power quality.
Electrical energy storage may be accomplished using battery technologies, capacitor storage systems, kinetic energy storage systems such as flywheels or potential energy storage systems. Battery technology for Lithium ion batteries, flow batteries and Rechargeable Sodium-Sulfur batteries (NaS) are improving but typically will provide estimated capability only in the range of 10 megawatts or less. Similarly, capacitive storage systems on reasonable scale only provide between 1-10 megawatts of capability. Flywheel storage systems are also typically limited to less than 10 megawatts due to physical size and structural materials constraints.
Conventional gravitational potential energy storage devices consist of mechanical lifting devices raising weights against the force of gravity and Pumped Storage Hydro, a method that stores energy in the form of water pumped uphill against the force of gravity. Mechanical lifting devices are limited in their height to a few hundred feet and therefore require large amounts of mass to store a significant amount of electric energy. This results in a very large cost, making these devices expensive and uneconomical. In Pumped Storage Hydro, water is pumped from a lower elevation reservoir to a higher elevation; the stored water is then released through turbines to convert the stored energy into electricity upon demand. The energy losses are typically greater than 20% of the amount stored and the difficulties in permitting, constructing and operating makes pumped storage hydro difficult to implement. It can take more than a decade to construct such a system.
Rail based energy storage systems have been disclosed for use in utility scale energy storage in U.S. Pat. No. 8,593,012 issued on Nov. 26, 2013, which provide very efficient electric energy storage. However, such systems are designed to operate on steep conventional rail grades with larger storage yards available at each end of the system. In certain geographic areas those steep conventional grade features may not be available.
It is therefore desirable to provide potential energy storage with capability in the range of 10-1,000 megawatts of power with high efficiency and reduced installation and capital investment requirements, which is operable with limited horizontal storage space on steeper than conventional rail inclines.